Added request cancellation functionality to the HTTP client.

[H-D-OWL]

Problem

While working with TgBot::TgLongPoll, I encountered an issue where long-polling and other HTTP requests could not be interrupted gracefully at any time (for example, during a graceful shutdown or during unexpected crashes).

Solution

A mechanism for safely canceling ongoing HTTP requests has been introduced. This allows the bot to immediately abort active network operations without waiting for the libcurl timeout to expire.

Key Changes

• HttpClient.h: Added the cancel() interface and atomic variables (_isEternalCancel and _cancelEpoch) for global management of request cancellation status. Also added isEternalCancelled() and getCancelExceptionText() for checking the cancellation status.

• CurlHttpClient.cpp: Cancellation logic implemented using CURLOPT_XFERINFOFUNCTION. The progress callback now returns a non-zero value when canceled, instructing libcurl to safely abort the transfer. The client now emits std::runtime_error containing cancelExceptionText and the name of the aborted request (e.g. request cancelled: getUpdates).

• Api.cpp: New cancellation capabilities integrated into Api::sendRequest.

[reo7sp]

Ok, thank you